Police found the gun they believe was used in the killings by Arnau’s body, which contained firearm discharge residue. Arnau had legally purchased the weapon Monday, according to authorities.

In a press conferenceTuesday, Lancaster County District Attorney Craig Stedman said he believed the children likely did not suffer through the killings.

“It appears they were shot in their sleep, and there would not have been any struggle, as pathetic as a comfort that that is,” Stedman said.

As for the blaze, investigators suspect that Arnau intentionally lit fires around the home and a garage, LancasterOnline reported.

Arnau had received mental health treatment prior to the incident, and she and her husband were going through a contentious divorce that had recently “escalated,” Stedman said.

Arnau filed for divorce in February 2016 and asserted that the marriage was “irretrievably broken,” according to court records obtained by LancasterOnline. Soon after, she requested a protection order against the husband, who she claimed was abusing her.

Arnau later sought to discontinue the protection order, records show.

The couple was temporarily sharing custody of the children pending resolution of the divorce case.

Police believe Arnau’s husband was at work at the time of the deaths and was not involved in the killings.